Biphasic recruitment of transcriptional repressors to the murine cytomegalovirus major immediate-early promoter during the course of infection in vivo

Our previous studies showed that establishment of murine cytomegalovirus (MCMV) latency in vivo is associated with repression of immediate-early gene expression, deacetylation of histones bound to the major immediate-early promoter (MIEP), changes in patterns of methylation of histones, and recruitment of cellular repressors of transcription to the MIEP. Here, we have quantitatively analyzed the kinetics of changes in viral RNA expression, DNA copy number, and recruitment of repressors and activators of transcription to viral promoters during the course of infection. Our results show that changes in viral gene expression correlate with changes in recruitment of RNA polymerase and acetylated histones to viral promoters. Binding of the transcriptional repressors histone deacetylase type 2 (HDAC2), HDAC3, YY1, CBF-1/RBP-Jk, Daxx, and CIR to the MIEP and HDACs to other promoters showed a biphasic pattern: some binding was detectable prior to activation of viral gene expression, then decreased with the onset of transcription and increased again as repression of viral gene expression occurred. Potential binding sites for CBF-1/RBP-Jk and YY1 in the MIEP and for YY1 in the M100 promoter (M100P) were identified by in silico analysis. While recruitment of HDACs was not promoter specific, binding of CBF-1/RBP-Jk and YY1 was restricted to promoters with their cognate sites. Our results suggest that sequences within viral promoters may contribute to establishment of latency through recruitment of transcriptional repressors to these genes. The observation that repressors are bound to the MIEP and other promoters immediately upon infection suggests that latency may be established in some cells very early in infection.